Tunguska event

Meteorite or comet

Date: June 30, 1908

Place: Tunguska, Siberia

Classification: 8 on the Torino Impact Hazard Scale; energy equivalent to at least 10 to 20 megatons of TNT released

Result: 2 dead, several nomad camps destroyed, more than 1,000 reindeer killed, 811 square miles (2,100 square kilometers) of forest flattened

Early on the morning of June 30, 1908, witnesses along a 621-mile (1,000-kilometer) path saw a fireball streak across the sky from the east-southeast. It was as bright as the Sun and cast its own set of shadows in the early morning light. The object exploded at 7:14 a.m., local time. Based upon seismic and barographic records, and upon the destruction caused, the explosion released energy equivalent to that of 10 to 20 megatons of TNT, making it the most devastating cosmic event on Earth during historical times. Depending upon the altitude of the explosion and the composition of the object, the energy released may have been as high as 50 megatons.

Had the explosion occurred over New York City, fatalities would have been in the millions. As it was, the object exploded over a sparsely inhabited forest in Siberia, roughly 43.5 miles (70 kilometers) north of Vanavara, a small village on the Stony Tunguska River. The region is one of primeval forests and bogs inhabited by nomads who tend large herds of reindeer. Near the epicenter (ground zero), trees burst into flame. Farther out, a great shock wave felled trees over an 811-square-mile (2,100-square-kilometer) area, pointing them radially outward, bottoms toward, and tops away from the epicenter. Right at the epicenter where the force of the blast wave was directly downward, a bizarre grove remained. Trees were left standing upright, but they were stripped of all their branches, like telephone poles.

An eyewitness in Vanavara said the sky was split apart by fire and that it was briefly hotter than he could endure. Because it was just after the summer solstice, the Sun remained above the horizon twenty-four hours a day north of the Arctic Circle. Dust, lofted high into the stratosphere, reflected so much sunlight back to the ground that even south of the Arctic Circle, in northern Europe and Asia, nights were not really dark for three days. People were amazed that they could read, or even take photographs, in the middle of the night. At least 1,000 reindeer were killed, and several nomad camps were blown away or incinerated. Some nomads were knocked unconscious, but remarkably, there are only 2 known human fatalities. An old man named Vasiliy was thrown 39 feet (12 meters) through the air into a tree. He soon died of his injuries. An elderly hunter named Lyuburman died of shock.

Scientists supposed that the seismic waves had been caused by an earthquake, but no scientists went immediately to investigate because of the remoteness of the site. It was not until 1927 that Leonid Kulik, the founder of meteorite science in Russia, reached the site after spending many days plunging through trackless bogs on horseback. Expecting to find a huge crater and a valuable nickel-iron mountain, Kulik and his assistant were amazed to find only a shattered forest stretching from horizon to horizon.

Careful research has since shown that the Tunguska object shattered about 5.3 miles (8.5 kilometers) above the ground. If it were a small comet, it must have been inactive, for there is no credible evidence of a tail. It must have been at least 328 feet (100 meters) in diameter and had an asteroidal core, because microscopic metallic particles were recovered that are more closely associated with asteroids than with comets. Russian scientists favor this hypothesis. The object’s trajectory and timing are consistent with it being a fragment of Comet Encke. Western scientists favor the possibility that it was a small, dark, rocky asteroid, perhaps 197 feet (60 meters) in diameter.

When a solid object of this size plunges into the atmosphere, it piles up air in front of it until the air acts like a solid wall. The object shatters, its kinetic energy is converted to heat, and the object vaporizes explosively. Microscopic globules form as the vapor condenses. Such globules have been recovered from peat bogs and tree resin at the site, as well as from ice layers in remote Antarctica. The cosmic dust cloud truly spread worldwide. These globules have more of the elements nickel and iridium than normal Earth rocks do—clear signatures of their cosmic origins.

For Further Information:

Chaikin, Andrew. “Target: Tunguska.” Sky and Telescope, January, 1984, 18-21.

Fernie, J. Donald. “The Tunguska Event.” American Scientist, September/October, 1993, 412-415.

Gallant, Roy A. “Journey to Tunguska.” Sky and Telescope, June, 1994, 38-43.

Verma, Surendra. The Tunguska Fireball: Solving One of the Great Mysteries of the 20th Century. Cambridge, England: Icon Books, 2006.

Zanda, Brigitte, and Monica Rotaru, eds. Meteorites: Their Impact on Science and History. Translated by Roger Hewins. New York: Cambridge University Press, 2001.